The objective of this study is to develop atomic absorption spectrophotometric (AAS) methodology for the quantitative analysis of aluminum in various adsorbed toxoids, vaccines and alum precipitated allergenic extracts. The aluminum is present at levels of 0.1 to 0.85 mg/ml. Aluminum phosphate, aluminum potassium sulfate and aluminum hydroxide are the materials used as adsorbents. In addition, information is to be gathered concerning the elemental composition of the toxoids containing the three different aluminum adjuvants and structural characterization of the aluminum adjuvant-antigen complex. Aliquots of samples which contained aluminum suspensions were acid digested with nitric and sulfuric acid and analyzed in the nitrous oxideacetylene flame of an atomic absorption spectrometer. The 396.2 nm aluminum line was used for analysis. The aluminum content of the National Bureau of Standards (NBS) Standard Reference Material No. 1075a aluminum 2 ethylhexanoate was determined to within 1% of the NBS certificate value by toxoids containing aluminum potassium sulphate and aluminum phosphate were compared with polarographic and inductively coupled argon plasma (ICP) emission spectrometry results. Reproducibility and recovery data for aluminum were determined for a variety of biological products containing aluminum phosphate, aluminum potassium sulphate and aluminum hydroxide adjuvants. In addition, ICP has been used to characterize the aluminum and potassium compositions of the precipitates and supernatant solutions which resulted from centrifugating toxoid suspensions that contained the three different aluminum adjuvants. Mass spectrometry will be explored as a method of determining structural information for the aluminum adjuvant-antigen complexes in the various adsorbed vaccines.